A portion of chimney inside this attic can tell us we have building issue on the exterior.

Efflorescence, the whitish coating, is a mineral deposit left behind as moisture in the brick evaporates on the surface. This often happens when chimneys have a missing or deteriorated rain cap.

The darker stain down the side is a water stain likely caused by the failure of a metal flashing on the exterior at the roofline.

Both issues allow moisture into the attic and possibly into your home.  This moisture can bring with it unpleasant odours, mildew, and mold. Left un-checked deterioration of finishes and structure can occur.